232 BIOLOGY OF PNEUMOCOCCUS 



cocci were not culpable in causing any ensuing pneumonia but that 

 the infection always came from without. 



The disappearance of members of the first three types during 

 convalescence and the subsequent appearance of organisms of a 

 heterologous group was early established by Dochez and Avery 

 (1915). 319 The authors stated that although pneumococci occur in 

 the mouths of 60 per cent of normal individuals, the organisms are 

 readily distinguishable from the highly parasitic types of pneumo- 

 cocci responsible for the severe forms of lobar pneumonia — a con- 

 vincing proof that infection in that disease is, in the majority of 

 instances, not autogenic in nature, but is derived from some ex- 

 traneous source. Dochez and Avery found further that in a high 

 percentage of instances healthy persons intimately associated with 

 cases of lobar pneumonia harbor the disease-producing types of 

 pneumococci. In every such instance the strain isolated from the 

 normal subject was found to correspond in type with that of the 

 infected individual with whom the healthy person had come in con- 

 tact. In conclusion, the authors stated that the existence of the 

 carrier state among healthy persons and among those recently re- 

 covered from pneumonia establishes a basis for understanding the 

 mechanism by means of which lobar pneumonia spreads and main- 

 tains its high incidence from year to year. 



The relative infrequency of pneumococci of the first three types 

 in the mouths of healthy persons of varying ages who gave no his- 

 tory of contact with pneumonia was also observed by Meyer 

 (1920). 899 Among one hundred normal individuals, no strains of 

 Type I or II (excepting an atypical II), and only three strains 

 of Type III pneumococci were found. Group IV organisms were 

 present in seventeen instances. In the sputum of fifty tuberculous 

 patients Lyall 841 found pneumococci in twenty cases. Excluding 

 one patient with a history of pneumonia in the previous year, 

 pneumococci of Type I occurred once, of Type II none were found, 

 of Type III three subjects harbored the organism, while pneu- 



